Process of lead cladding



No Drawing.

United States Patent ()fifice 3,107,858 Patented Feb. 2, 1965 3,167,858 PROCESS OF LEAD (CLADDKNG Victor E. Knapp, Roslyn, N.Y., and Neil E. Ritehey,

Chester County, Pa, assignors to Knapp Miils incorporated, Long Island City, N.Y., a corporation of New York Filed Dec. 22, 1959, Ser. No. 361,198 12 Claims. ((11. 29-487) The present invention relates to the cladding of lead on sheets of copper, aluminum, iron and. their alloys. It has been found that these metals can be cladded with lead so as to form a bonded sheet which is useful for shielding against the harmful effects of radiation or corrosion. In the following description of the invention, the particular metal which is to be clad will be called the basic metal, with the understanding that it may either be steel, copper, aluminum, or alloys thereof. This application is a continuation in part of our application No. 686,876 filed September 30, 1957, and now abandoned.

Lead cladded metal structures are becoming increasingly important in radiation shielding. Until the present invention, no completely satisfactory method has been evolved to effect the bonding of lead to these metals in a wide range of thicknesses and by a reliable and relatively easily performed commercially practical method.

According to the present invention, a method is disclosed which permits the creation of a strong metallurgical bond between the lead and a basic metal so as to form lead clad metal sheets or plates wherein the lead and the basic metal are so tightly bonded together that the sheets or plates may be bent, cut, shaped, or otherwise handled without any separation of the two metals.

Accordingly, an object of the present invention is to provide an improved method of cladding a basic metal with lead.

Another object of the present invention is to provide an improved lead clad basic metal.

Another object of the present invention is to provide an improved method of metallurgically bonding a basic metal and lead together.

Another object of the present invention is to provide a practical and reliable method of bonding lead to a basic metal which is suitable for commercial use.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

The first step in the process comprises the coating or plating with nickel of the basic metal surface which is to be clad with lead. The coating of the basic metal with the nickel may be accomplished by any of the known types of nickleplate, such as electroplating or chemical plating.

A preferred chemical process which provides a bond between the nickel and the basic metal is accomplished by a controlled catalytic reduction of nickel in a plating bath. In such a bath, the basic metal parts are immersed in a hot solution containing a chemical reducing agent, such as sodium hypophosphite and a buffered solution of nickel salt, such as nickel chloride.

Suitable solutions for such a chemical plating of nickel have also been disclosed in United States Patents Nos. 2,658,841 and 2,658,842 which issued to Gutzeit and Kreig, Patent No. 2,694,017 which issued to Rischan and Kreig, and Patent No. 2,694,019 which issued to Gutzeit. The plate solutions which were disclosed in these patents may be applied by the process described more completely in PatentsNo. 2,658,839 which issued to P. Tallmey et al., No. 2,717,218 which issued to P. Tallmey et al., No.2,762,723 which issued to Tallmey and Gutzeit, and No. 2,766,138 which issued to Paul Tallmey. These patents disclose processes for depositing nickel on the basic metals. The coatings which result from these processes are not in all cases pure nickel. They may, for example, include phosphides. The presence of these additional elements in the coatings have been found to have no adverse affect upon the lead cladding process and in the case of the phosphides, their pres ence in the nickel coats has been found to provide improved adherence between the lead and the basic metal for reasons which at this time are not clearly understood.

The nickel coating is preferably thicker than .0005". A coating thickness of .001" has provided a satisfactory bond.

After the basic metal has been nickel-plated, the nickel is tinned with a mixture of lead and tin or antimony. A preferred tinning mixture comprises about 41 percent lead and 59 percent tin which is melted to permit dipping of the nickel-plated surface into the tinning mixture. The melting point for the 41 percent lead and the 59 percent tin mixture is about 360 F. The basic metal is preferably fluxed with one of the suitably known fluxes for the bonding of tin to the particular basic metal prior to the tinning.

The tinning of the basic metal having been completed, I

the metal is ready to receive the lead to which it is to be bonded. Several methods may be utilized to bring the lead in contact with the tinned surface of the basic metal. Each of them makes use of the principle that the lead-tin eutectic coating must first be melted before the lead metal will adhere to it.

In the lead burning method, the lead may be hand deposited on the basic metal by simply burning a bar of lead over the basic metal. Thus the lead melts and flows by gravity so that it spreads over the tinned basic metal surface. The burning may be accomplished with any heating implement capable of furnishing a sufficiently high temperature to melt the lead, as with a torch operated with hydrogen or propane gas, for example.

As the lead is spreading over the tinned surface, a workman plays over the surface with a torch, and fuses the lead into the tinned surface. The high temperature of the lead and the heat from the torch are more than is necessary to heat the eutectic coating so that it becomes largely or completely liquified. The above procedure may be continued until the entire surface has been coated with lead. Additional layers of lead may be deposited in a similar fashion to increase the overall thickness by repeating the same operation with new quantities of lead metal.

Another method of bringing the lead into contact with the basic metal surface is called the pour-bonding method. In this method, after the basic metal has been tinned, as above, it is preheated to about 400 F. Meanwhile, lead metal has been heated to a temperature of 700 to 750 F., so that it is now entirely molten. The lead, is then simply poured over the tinned basic metal occurs during the bonding operation inthe press.

total heating time for both periods should be kept below a i I 8,167,858

surface to anythickness required. ,As the molten lead i comes into contact with the tinned surface of the basic metal, it forms a homogenous mass with the eutectic coating which has melted under the vheat applied so a that an excellent. bond with the basic metal isproduced.

with the tinned basic metal surface in solid form, usu-,

ally as sheets, by what is called the roller or platens pressure method. In this method, after the basic metal surface has been nickel-platedand tinned, the surface of the lead which is to be bonded to the basiometalis cleaned to remove lead oxide by scraping or other suitable cleaning 'methods'and the cleaned basic metal .sur-,

face is also tinned; As the basic metal must be heated i seen in the table below which includes excerpts from regfor the bonding, the basic metal slab is preferably heated prior to the tinning. The bonding temperatures are slightly above the meltingpoint of tin. Lead eutectic alloy is used to tin both the lead and the basic metal so tht the lead is heated 40 F; above the 360 F.

melting point for the tin-lead-alloy. Thelead is now tinned. A preferred method of tinning thelead is by hand wiping using an oxygen-hydrogen torch to apply heat as needed.

The basic metal and lead sheets or plates are bonded together under pressure by means of either platens or.

rollers. Preferably, the platens or rollers which serve to press the lead andthe basic metal are heated to the bonding temperature so that the bonding temperature will be maintained during the required pressure period.

. The platens, for instance, may be heated to about 400 F. prior .to the insertion of the lead and the basio'metal therebetween. After the lead has been tinned, it is reheated, if necessary, to about 400 F. and the nickel.

coated and tinned face of the basic metal is placed as the case maybe.

Suificient pressure is applied to insure a tight engagew.

ment of the two tinned surfaces. Where aluminum hasbeen used as a basic metal, a pressure of about 15 psi. has been found to besatisfactory. The pressure is. maintained for asufiicient period to insure the forma-.

tion of the bond. For instance, with aluminum, when the preferred pressure of 15 psi. is used, a pressure period of two minutesis preferred. At the end of this period, the lead and basic metal are cooled while still under pressure to solidify the interface. This may be doneby a suitable water spray. Thereafter, the pressure is released. to permit the removal of the bonded metals.

In the particular case of bonding aluminum to lead, where the aluminum has been hardened or otherwise treated for increased strength, it is necessary to limit the heating of the aluminum during the bonding to an amount which will not cause over-aging of the heat treated aluminum. It is well known that where heat treated alloys are subjected to heat, a time is reached when the strengths of the aluminum alloys begin to dev or the aluminum alloy is heated twice in the above-described process to a temperature of'about 400 F; The first heating is'in the tinningbath and the second heating The two minutes, a total time of three minutes resultsfl As ular over-aging tables, this is a suitable short time to prevent over-aging for each of the aluminum alloys listed. The total heat time for each of the aluminum alloys listed should not be exceeded. 0

Maximum Time Before Overaging Temperature,

v Aluminum Alloy Degrees F.

15 sec.

30 sec.

3 min;

10 min. 20 hours. 15 sec.

30 sec.

2 min.

. 5 min.

30min.

2024-186 and 6061-536";

It: will seenthat the present invention provides an improvedmethod for metallurgically bonding lead to sheets or plates of a basic metal which may be copper, aluminum, iron or their alloys. The method of the present invention provides an improved lead clad basic metal in which an extremely tightlbond is formed between the basic metal and the lead. The finished bonded sheets may be subjected. to. additional manufacturing processes such as bonding, cutting, and. shaping, without a failnre'of the bond. The process is relatively simple and is reliable .so that it is suitable for commercial usage on a large scale to provide numerous lead cladded metal productsin the constantly growing market for such products. It has beenv found that the lead clad basic metal as-formed by the process of the present invention in many cases has a tensile strength which is greater than would be expected .fmmthe combined strengthso-f the lead and basic metal and that there is' an'unexpected and important increase in the strengthyof the finished product which results from the practice of thecladding process of the invention.

As various changes may be made in the form, construction, and arrangement of the parts herein without departing from-the spirit and scope-of the invention and without sacrificing any of its advantages, it is to. be understood that allmatter herein is to be interpreted as illustrative and not in a limiting sense.

Similarly, it is to be understood that .the'mention of any metal is intended to include any of its alloys as of copper, aluminum, iron, and their alloys, which comprises the steps of coating a surface of the-basic metal sheet with nickel, applying a tin-lead eutectic to the nickelcoated surface of the basicmetal sheets, ap-

- plying a tin-lead eutectic coat to a surface'of. the lead sheets at least partially melting the said eutecticcoatings, Y

pressing the eutectic coated surface of the lead sheets and the basic metal sheets together, cooling the basic metal and the lead while subjected to the pressure, and

thereafter removing thepressure from the basic metal eutectic coatings are melted by the heating of the lead sheets to a temperature of about 400*F. prior to-the pressing together. ofthe lead and basic metal.

5.-The process as claimed in claim 1 in which the pressing step is performed by'a rolling action.

6. The process as claimed in claim 4 in which said eutectic coated surfaces are pressed together under a pressure of about 15 psi. for a period of about two minutes.

7. The process of metallurgically bonding sheets of lead to sheets of a basic metal included in the group consisting of copper, aluminum, iron, and their alloys, which comprises the steps of chemically coating a surface of the basic metal sheets with nickel, applying a tin-lead eutectic coating to the nickel coated surface of the basic metal sheets, applying a tin-lead eutectic coating to a surface of the lead sheets, at least partially melting the said eutectic coatings, pressing the eutectic coated surfaces of the lead and the basic metal sheets together, cooling the basic metal and lead sheets, and thereafter releasing the pressure.

'8. The process as claimed in claim 7 in which the basic metal is aluminum and the nickel plating of the aluminum sheets comprises a controlled catalytic reduction in a hot bath comprising a chemical reducing agent and a nickel salt.

9. The process as claimed in claim 8 in which the nickel salt comprises nickel chloride and the chemical reducing agent comprises sodium hypophosphite whereby the nickel coating comprises about 8-12 percent phosphorus and about 91-88 percent nickel.

10. The process of metallurgically bonding solid lead to solid aluminum which comprises the steps of coating a surface of the aluminum with nickel to a depth of at least .0005 inch by a controlled catalytic reduction in a hot bath containing a chemical reducing agent and a nickel salt, applying a-tin-lead eutectic coat to the nickel coated surface, applying a tin-lead eutectic coat to a surface of the lead, at least partially melting the said eutectic coatings, pressing the eutectic coated surfaces together, cooling the aluminum and the lead while subjected to the pressure, and thereafter releasing the pressure.

11. The process as claimed in claim 10 in which the nickel salt comprises nickel chloride and the chemical reducing agent comprises sodium hypophosphite whereby the nickel coating comprises about 8 to 12 percent phosphorus and about 92 to 88 percent nickel.

12. The process of metallurgically bonding relatively thick sheets of solid lead to solid rigid aluminum which comprises the steps of coating a surface of the aluminum with nickel to a depth of at least .0005 inch by a controlled catalytic reduction in a hot bath containing a chemical reducing agent and a nickel salt, thereafter applying a tin-lead eutectic coat to the'nickel coated surface, applying a tin-lead eutectic coat to a surface of the lead sheets, at least partially melting both of the said eutectic coatings, pressing the eutectic coated surfaces together, and simultaneously cooling the aluminum and the lead while subjecting them to the pressure, thereafter releasing the pressure, and said nickel salt comprising nickel chloride and the chemical reducing agent comprising sodium hypophosphite whereby said nickel coating comprises about 8 to 12 percent phosphorus and about 88 to 92 percent nickel.

References Cited in the file of this patent UNITED STATES PATENTS 440,952 Land Nov. 18, 1890 1,079,035 Tebbetts Nov. 18, 1913 1,280,908 Wales et al. Oct. 8, 1918 1,996,657 Shannon Apr. 2, 1935 2,174,733 Chace Oct. 3, 1939 2,694,017 Reschan et al Nov. 9, 1954 2,746,136 Richaud May 22, 1956 2,795,040 Antel et al. June 11, 1957 2,824,365 Erickson Feb. 25, 1958 2,837,818 Storcheim June 10, 1958 2,841,546 Robinson July 1, 1958 2,887,766 Fike et al. May 26, 1959 2,982,017 Drummond May 2, 1961 FOREIGN PATENTS 624,369 Great Britain June 7, 1949 OTHER REFERENCES Aluminum Soldering, Supplement to the Journal of The American Welding Society, September 1940, pp. 320-s and 321-s. 

1. THE PROCESS OF METALLURGICALLY BONDING LEAD SHEETS TO SHEETS OF BASIC METAL INCLUDED IN THE GROUP CONSISTING OF COPPER, ALUMINUM, IRON, AND THEIR ALLOYS, WHICH COMPRISES THE STEPS OF COATING A SURFACE OF THE BASIC METAL SHEET WITH NICKEL, APPLYING A TIN-LEAD EUTECTIC TO THE NICKEL COATED SURFACE OF THE BASIC METAL SHEETS, APPLYING AT LEAST PARTIALLY MELTING THE SAID EUTECTIC COATINGS PRESSING THE EUTECTIC COATED SURFACE OF THE LEAD SHEETS AND THE BASIC METAL SHEETS TOGETHER, COOLING THE BASIC METAL AND THE LEAD WHILE SUBJECTED TO THE PRESSURE, AND THEREAFTER REMOVING THE PRESSURE FROM THE BASIC METAL AND THE LEAD SHEETS. 